JPH11124536A - Water-base coating agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-base coating agent that can form films to which rain-striped dirt is hardly adherent or from which the dirt is easily washed out even if it adheres to the films. SOLUTION: The coating agent is formed by emulsifying/dispersing in an aqueous medium a graft copolymer comprising a unit based on the following macromonomer as a branch polymer and a vinyl polymer composed of (meth) acrylic ester monomer units and, if necessary, other radical-polymerizable monomer units as a backbone polymer; macromonomer: a macromonomer with a number average molecular weight of 1,000-30,000 formed by bonding a radical- polymerizable polymer group to one end of a polymer comprising perfluoroalkyl (meth)acrylate unit (a), polyalkylene glycol mono(meth)acrylate unit (b), and other radical-polymerizable monomer unit (c), the proportion of each monomer unit based on the total weight of all the monomer units being 20-70 wt.% for unit (a); 30-80 wt.% for unit (b); and 0-40 wt.% for unit (c).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous coating agent of the type in which polymer particles are dispersed in an aqueous medium. In the present invention, the present invention relates to a graft having a branched polymer having a specific structure as the polymer. Since the copolymer is used, there is a feature that the surface of the coating film is not easily stained by floating substances in the air.

[0002]

2. Description of the Related Art In recent years, water-based paints, which are harmless to the human body and do not pollute the environment, have been used in place of solvent-based paints, reflecting the recent rise in environmental awareness. However, in the case of water-based paints, it is necessary to set the glass transition point of the resin low in order to impart film forming properties, and as a result, there is a problem that the coating film of the water-based paint is soft and dirt attached to the film is difficult to remove. . As a means for improving the weather resistance and stain resistance of the coating film, a method of adding only a small amount of a block polymer or a graft polymer and modifying only the surface properties of the coating film is known. In the field of paint, a graft polymer having a polymer segment having a low surface energy, such as a perfluoroalkyl group or silicone, is often used in order to impart water repellency and stain resistance to the coating film surface.

[0003] That is, JP-A-56-163183 discloses that a methacrylate-based polymer containing at least 70% of perfluoro (meth) acrylate is used as a branch segment, and a copolymer of an alkyl acrylate such as ethyl acrylate and a hydroxyalkyl (meth) acrylate is used. A water / oil repellent comprising a graft copolymer having a polymer as a trunk segment is disclosed. JP-A-57-180680 discloses that a graft copolymer having a perfluoroalkyl group as a branch and a diene-based monomer copolymer as a trunk is used as a water- and oil-repellent agent having excellent film-forming properties at low temperatures. In addition, Japanese Patent Application Laid-Open No. 9-67417 discloses a fluorine-based graft copolymer having a branch segment of a specific composition and less foaming.

The properties of the surface of the coating film obtained by the above-mentioned means are mainly water repellency, but water repellency is a problem in water-based paints composed of the above-mentioned resin having a low glass transition temperature.
Prevention of rain streak cannot be expected. In order to prevent such rain streak-like stains in the water-based paint, conventionally, a technical means of making the surface of the coating film hydrophilic has been adopted. However, when the coating film is made hydrophilic by conventional means, it is difficult to maintain the stain resistance for a long period of time because the added hydrophilic substance is easily desorbed by rainwater or the like.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous coating agent which forms a film which is hard to adhere to rain streak-like stains or which is easily washed away even if it does.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a polymer composed of a specific hydrophilic unit and a hydrophobic unit is used as a branch polymer and has a structure suitable for forming a film. The present inventors have found that an aqueous coating agent comprising a graft copolymer having a vinyl polymer as a trunk polymer can provide a film which is less likely to have rain streak stains, and has completed the present invention. That is, the present invention relates to a graft copolymer wherein a unit composed of the following macromonomer is used as a branch polymer, and a polymer composed of a (meth) acrylate monomer unit and optionally another radically polymerizable monomer unit is used as a trunk polymer. An aqueous coating agent obtained by emulsifying and dispersing a polymer in an aqueous medium. Macromonomer: (a) a perfluoroalkyl (meth) acrylate unit, (b) a polyalkylene glycol mono (meth) acrylate unit and (c) another radically polymerizable monomer unit, and the total of all monomer units The proportion of each monomer unit based on the amount is (a) unit;
70% by weight, (b) unit; 30 to 80% by weight, and (c) unit: 0 to 40% by weight having a radical polymerizable group at one end of a polymer and having a number average molecular weight of 1,000 to 3;
000 macromonomer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The graft copolymer in the present invention is obtained by copolymerizing a macromonomer and a monomer mixture comprising a (meth) acrylate monomer and, if desired, another radically polymerizable monomer. As described above, the components constituting the skeleton of the macromonomer include (a) a perfluoroalkyl (meth) acrylate unit, (b) a polyalkylene glycol mono (meth) acrylate unit, and (c) other radically polymerizable monomers. Is a unit.

Further, as described above, the content ratio of the units (a), (b) and (c) in the macromonomer is, based on the total amount of these units, (a) units; 70% by weight, (b) unit; 30
0 to 80% by weight and (c) unit; 0 to 40% by weight, more preferably, (a) unit; 25 to 60% by weight, (b) unit; 40 to 75% by weight and (c) unit;
0 to 30% by weight. When the proportion of the unit (a) in the skeleton portion of the macromonomer is less than 20% by weight, the stain resistance of the film surface formed when used as a coating agent is insufficient, while exceeding 70% by weight. However, the stain resistance of the coating surface is insufficient. (B) The unit ratio is
If the amount is less than 30% by weight or exceeds 80% by weight, the stain resistance of the coating surface is insufficient. Further, even if the proportion of the unit (c) exceeds 40% by weight, the stain resistance of the coating surface becomes insufficient.

In the present invention, the macromonomer forms a branch copolymer of the graft copolymer which is a main component of the aqueous coating agent. When the coating agent is applied to the substrate, the branch polymer appears on the surface of the coating film due to the properties of the perfluoroalkyl (meth) acrylate unit contained therein, and accordingly, the hydrophilic polymer derived from the unit (b) is produced. Alkylene glycol units also appear on the coating surface, rendering the surface hydrophilic. It is presumed that the hydrophilicity is imparted to the film surface as described above, thereby exhibiting stain resistance.

The (a) perfluoroalkyl (meth) acrylate preferably has a perfluoroalkyl group having 3 to 15 carbon atoms, more preferably has a perfluoroalkyl group having 6 to 12 carbon atoms. Specifically, a compound represented by the following chemical formula is exemplified. _{CF 3 CH 2 OCOC (CH 3} ) = CH 2 CF 3 CF 2 CH 2 OCOCH = CH 2 CF 3 (CF 2) 4 CH 2 OCOC (CH 3) = CH 2 CF 3 (CF 2) 5 (CH 2) _{2 OCOC (CH 3) = CH} 2 CF 3 (CF 2) 6 (CH 2) 2 OCOC (CH 3) = CH 2 CF 3 (CF 2) 7 (CH 2) 2 OCOCH = CH 2 CF 3 (CF 2 ) ₇ (CH ₂ ) ₂ OCOC (CH ₃ ) = CH ₂ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₄ OCOC (CH ₃ ) = CH ₂ (CF ₃ ) ₂ CF (CF ₂ ) ₅ (CH ₂ ) ₂ OCOCH = C
_{H 2 (CF 3) 2 CF} (CF 2) 6 (CH 2) 3 OCOCH = C
_{H 2 (CF 3) 2 CF} (CF 2) 8 (CH 2) 3 OCOCH = C
_{H 2 (CF 3) 2 CF} (CF 2) 10 (CH 2) 3 OCOCH = C
_{H 2 (CF 3) 2 CF} (CF 2) 6 CH 2 CH (OH) CH 2 O
COCH = CH ₂

(B) Polyalkylene glycol mono (meth) acrylate is a compound in which a (meth) acryloyl group is bonded to one end of polyalkylene glycol,
Its preferred number average molecular weight is 160-5000.
As the polyalkylene glycol, polyethylene glycol and polyisopropylene glycol are preferable. In the present invention, as described above, the phenomenon that the polyoxyalkylene unit forming the branch copolymer of the graft copolymer appears on the surface of the coating film together with the perfluoroalkyl (meth) acrylate unit to make the surface hydrophilic is described. It is used to prevent pollution. Therefore, a compound having a polyalkylene glycol unit and a radical polymerizable group which can be expected to have the same effect as the above polyalkylene glycol mono (meth) acrylate, such as a methoxy group, an ethoxy group or a propoxy group at one end of the polyalkylene glycol. A compound having a suitable lower alkoxy group and a (meth) acryloyl group at the other end may be used as the component (b).

(C) Other radically polymerizable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth) T-butyl acrylate, (meth)
Cyclohexyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, (meth)
Examples include stearyl acrylate, styrene and acrylonitrile, and these monomers may be used alone or in combination. Among these, preferred monomers from the viewpoints of copolymerizability and film properties of the obtained coating agent are methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. Ibutyl, t-butyl (meth) acrylate, (meth)
Cyclohexyl acrylate and (meth) acrylic acid 2
-Ethylhexyl.

A macromonomer is synthesized by bonding a radical polymerizable group such as a (meth) acryloyl group, a styryl group and an allyl group to one end of a polymer obtained by copolymerizing the above monomer and the like. You. As a method for synthesizing a macromonomer, a method as outlined below can be employed. First, in a polymerization system using a carboxyl group-containing mercapto compound such as mercaptoacetic acid or mercaptopropionic acid as a chain transfer agent, radically polymerizing a monomer to form a skeleton of a macromonomer, and having a carboxyl group at a terminal. Obtain a prepolymer. Then
A macromonomer can be synthesized by a method of adding an epoxy group-containing monomer such as glycidyl (meth) acrylate to the prepolymer. The molecular weight of the macromonomer is a number average molecular weight in terms of polystyrene determined by gel permeation chromatography,
0000, and more preferably 2,000 to 10,000.
0. If the number average molecular weight of the macromonomer is less than 1,000, the coating agent obtained is poor in stain resistance, while if it exceeds 30,000, the polymerizability of the macromonomer is poor and unreacted macromonomer is contained in a large amount in the coating agent. As a result, the physical properties of the coating are inferior.

Next, a monomer to be copolymerized with the above-mentioned macromonomer (hereinafter referred to as a copolymerized monomer) will be described. In a graft copolymer obtained by copolymerizing a comonomer with a macromonomer, a trunk polymer portion is formed by a comonomer unit. In the present invention, a (meth) acrylate alone or a (meth) acrylate and another radically polymerizable monomer are used together as a comonomer. The preferred copolymerization ratio of the macromonomer and the copolymerization monomer is such that the ratio of the branch component derived from the macromonomer in the obtained graft copolymer is 0.1 to 20% by weight. If the proportion of the branch polymer in the graft copolymer is less than 0.1% by weight, the coating formed from the graft copolymer tends to be insufficient in stain resistance, while if it exceeds 20% by weight, the water resistance of the coating is poor. Easy to inferior.

Specific examples of the (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, cyclohexyl (meth) acrylate, and (meth) acrylic acid 2 Alkyl (meth) acrylates, such as ethylhexyl, lauryl (meth) acrylate and stearyl (meth) acrylate;
And 2-hydroxyethyl (meth) acrylate,
2-hydroxypropyl (meth) acrylate, (meth)
Perfluoroalkyl acrylate, glycidyl (meth)
Acrylate and N, N-diethylaminoethyl (meth) acrylate are exemplified. These can be used alone, but usually a plurality of types are used in combination so as to balance the properties of the coating film. It is preferable that 50% by weight or more of the comonomer is a (meth) acrylic acid ester from the viewpoint of excellent film formability of the graft copolymer.

The radical polymerizable monomers other than (meth) acrylic acid esters include vinyltrimethoxysilane,
Vinylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldi Monomers having a hydrolyzable silyl group such as ethoxysilane, vinyltripropoxysilane, vinylmethyldipropoxysilane, γ-methacryloxypropyltripropoxysilane and γ-methacryloxypropylmethyldipropoxysilane; (meth) acrylonitrile, Acrylamide, (meth) acrylic acid, maleic acid or maleic anhydride, itaconic acid, vinyl acetate, vinyl propionate, styrene, α-methylstyrene and the like can be mentioned. These can be used alone or in combination of two or more.

Among the above copolymerizable monomers, from the viewpoint of copolymerizability and physical properties of the resulting coating film, alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms and hydrolyzable silyl group are preferred. Preferred are monomers having styrene, hydroxyalkyl (meth) acrylate having an alkylene group having 2 to 3 carbon atoms, (meth) acrylic acid and glycidyl methacrylate. By using a monomer having a hydrolyzable silyl group in combination, a self-curing polymer is obtained, and such a polymer is formed into a cured coating film at room temperature. As another means for obtaining a cured coating film, a method of using a hydroxyl group-containing graft copolymer as a graft copolymer and combining it with a curing agent such as a polyvalent isocyanate or an amino resin, or other known high-molecular weight copolymers is used. There is molecular curing means.

As a method for copolymerizing the macromonomer and the comonomer, a method such as a solution polymerization method, an aqueous emulsion polymerization method or an aqueous suspension polymerization method can be employed, but a polymerization method using an aqueous polymerization medium is preferred. The aqueous polymer dispersion obtained by polymerizing the above components in an aqueous polymerization medium can be used as it is as an aqueous coating agent. A particularly preferred polymerization method is a method in which micro-sized suspended particles are dispersed in water, which is sometimes referred to as a micro-suspension polymerization method. According to such a method, the macromonomer can be uniformly copolymerized with the comonomer in an aqueous medium, and there is almost no generation of a grid during the polymerization. In the microsuspension polymerization method, a solution in which an oil-soluble radical initiator is dissolved in a monomer mixture is dispersed (pre-emulsion) in an aqueous medium with a particle size of 0.02 to 2.0 μm, and the temperature is raised and Polymerize. Usually, the polymerization temperature is preferably from 50 to 100C, and the polymerization time is preferably from 3 to 10 hours. Further, the preferred weight ratio of the monomer-dispersed particles in the aqueous medium is 10 to 60.
% By weight.

The oil-soluble radical initiator preferably has a solubility in water at 20 ° C. of 10% by weight or less.
Specifically, 2,2′-azobisisobutyronitrile,
2,2'-azobis-2,4-dimethylvaleronitrile, methyl-2,2'-azobisisobutyrate, lauroyl peroxide, benzoyl peroxide, dicumyl peroxide, t-butyl peroxypivalate, etc. Is mentioned. In producing the pre-emulsion, various surfactants such as anionic or nonionic surfactants used in general aqueous emulsion polymerization can be used. A surfactant having a radically polymerizable group is preferable from the viewpoint of improving the water resistance and weather resistance of a film formed by the obtained aqueous coating agent. Preferred number average molecular weight of the graft copolymer obtained by the above polymerization is 2000 to 500,
000.

The aqueous coating agent of the present invention is used for fillers such as clay, talc, calcium carbonate, titanium white and colloidal silica, pigments, dyes, film-forming aids, plasticizers, wetting, dispersing and defoaming. Various surfactants,
An appropriate amount of an ultraviolet absorber, an antibacterial agent, a rust inhibitor and the like may be added as necessary. When using a graft copolymer having a hydrolyzable silyl group, an organic tin compound such as dibutyltin laurate or an acidic compound may be added as a catalyst to promote a curing reaction by the hydrolyzable silyl group. preferable. When a graft copolymer having a hydroxyl group as a cross-linking functional group is used, it is preferable to use a polyisocyanate or an amino resin as a curing agent.

The substrate to which the aqueous coating agent is applied includes glass, slate, metal, wood, plastic and the like. For the purpose of use, exterior building paint that is hard to get streak stains, acid rain paint, antifouling paint, inorganic building material water repellent, electric and electronic component moistureproof coating,
Examples include a magnetic tape back coat agent and a fiber treatment agent. Hereinafter, the present invention will be described more specifically with reference to Reference Examples, Examples, and Comparative Examples. In addition, all the parts of the component blend in each example are parts by weight.

[0022]

Reference Examples 1 to 3 (Synthesis of Macromonomer) Stirrer, Two Dropping Funnels,
In a flask equipped with a gas inlet tube, thermometer and condenser,
30 g of the monomer mixture shown in Table 1, 2.12 g of mercaptopropionic acid as a chain transfer agent, and 21 g of butyl acetate were charged.
The temperature was raised to ° C. Thereafter, a mixed solution consisting of 70 g of the monomer mixture and 45 g of butyl acetate was added dropwise over 2 hours from one dropping funnel, and 1.3 g of azobisisobutyronitrile was added to 34 g of butyl acetate from the other dropping funnel.
Was added dropwise over 5 hours. Thereafter, the reaction was further continued for 1 hour, and then the polymerization reaction was completed. By the above operation, a butyl acetate solution of a polymer having a carboxyl group derived from a chain transfer agent at one end of the molecule was obtained.

To the obtained polymer solution, 0.02 g of hydroquinone monomethyl ether, 1.0 g of tetrabutylammonium bromide and 3.0 g of glycidyl methacrylate were added.
By reacting the carboxyl group at the polymer terminal with the glycidyl group of glycidyl methacrylate over time, a macromonomer having a methacryloyl group introduced at the terminal was obtained with a purity of 95% or more.

[0024]

[Table 1]

The abbreviations for the monomers shown in Table 1 represent the following compounds, respectively. FMA: Perfluorooctylethyl methacrylate PE-350: Blenmer PE-350 (polyethylene glycol monomethacrylate having 7 to 9 oxyethylene units) (manufactured by NOF Corporation) MMA: methyl methacrylate

[0026]

Example 1 (1) Preparation of Monomer Emulsion As a monomer, MMA; 50 parts, n-butyl acrylate; 30 parts, hydroxyethyl methacrylate;
Parts, γ-methacryloxypropyltriethoxysilane;
Using 10 parts of the macromonomer of Reference Example 1 and 0.2 part, the following raw materials were emulsified and dispersed with a homomixer to prepare a monomer emulsion. Emulsifier: Anionic surfactant having a sulfoammonium group at the end of the polyoxyethylene chain of the alkylphenol polyoxyethylene adduct ───0.7 parts Initiator: azobisisobutyronitrile ───0.33 parts aqueous Medium: deionized water ───60 parts pH buffer: baking soda ───1 part

(2) Polymerization Step A flask equipped with a stirrer, a thermometer and a cooler was charged with 80 parts of deionized water and 2 parts of an emulsifier. The emulsion was added dropwise over 3 hours. After the completion of the dropwise addition, the temperature of the solution was raised to 90 ° C., and the polymerization was further continued for 1 hour, and then the polymerization was stopped. During the polymerization, no liquid separation or blocking occurred, and the polymerization was carried out stably. The average particle size of the obtained polymer-dispersed particles was 0.25 μm, and the pH of the reaction solution was 9.0.

The tripropylene glycol n-butyl ether 10 per 100 parts of the obtained polymer emulsion
In addition, a coating liquid was prepared. The obtained coating liquid was applied on a chromate-treated aluminum plate using a bar coater, and after drying, a coating film having a thickness of 16 μm was formed. After the obtained test piece was cured in an atmosphere of 23 ° C. and 40% RH for 2 weeks, the physical properties of the coating film were measured. The results are as shown in Table 2.

[0029]

Example 2 An aqueous emulsion of a graft copolymer was obtained in the same manner as in Example 1, except that the copolymerization ratio of the macromonomer was changed to 0.7 part. Using the emulsion, a coating liquid was prepared in the same manner as in Example 1, and the physical properties of the coating film formed from the coating were measured. The results are as shown in Table 2.

[0030]

Examples 3 to 4 The same procedures as in Example 1 were carried out except that 0.7 part of the macromonomer obtained in Reference Example 2 (corresponding to Example 3) or Reference Example 3 (corresponding to Example 4) was used. hand,
An aqueous emulsion of the graft copolymer was obtained. Hereinafter, the physical properties of the coating film obtained by the same operation were measured.

[0031]

Comparative Example 1 An aqueous emulsion of a graft copolymer was obtained in the same manner as in Example 1 except that no macromonomer was used. Hereinafter, the physical properties of the coating film obtained by the same operation were measured.

[0032]

[Table 2]

The methods for measuring various physical properties shown in Table 2 are as follows. Pencil hardness: according to the method described in JIS K5400, section 8.4.2. -Flexibility: According to a method according to the method described in JIS K5400 8.1 (evaluated at a diameter of 10 mm). -Adhesiveness: After the cut of the lumps (10 x 10 = 100 pieces), the cellophane tape was peeled off, and the number of remaining lumps was evaluated. -Water resistance: The appearance was evaluated by immersing the coated pieces in boiling water for 1 hour. -Contact angle with water: (1) The contact angle between the cured coating film and water was measured with a goniometer. (2) The cured coating film was immersed in water for one day, and the contact angle between the dried coating film and water was measured. Stain resistance: Using a commercially available aluminum plate coated with a white paint, the coating agent obtained in each example was applied on a white paint film in the same manner as in Example 1 to form a paint film. After curing for two weeks, it was left outdoors for three months, and the state of contamination during that time was measured with a color difference meter. The evaluation was made by the difference (−ΔL) between the initial L value and the L value after the outdoor exposure test.

[0034]

As is evident from the stain resistance data in Table 2, according to the aqueous coating agent containing a graft copolymer having a specific structure according to the present invention as a main component, a film having excellent stain resistance can be obtained. Can be formed.

Continuation of the front page (72) Inventor Takehisa Yamamura 1 in Funamicho, Minato-ku, Nagoya-shi, Aichi, Japan

Claims (2)

[Claims] 1. A graft copolymer comprising a unit based on the following macromonomer as a branch polymer and a polymer comprising a (meth) acrylate monomer unit and optionally another radically polymerizable monomer unit as a trunk polymer. An aqueous coating agent obtained by emulsifying and dispersing the coalesced particles in an aqueous medium. Macromonomer: (a) a perfluoroalkyl (meth) acrylate unit, (b) a polyalkylene glycol mono (meth) acrylate unit and (c) another radically polymerizable monomer unit, and the total of all monomer units The proportion of each monomer unit based on the amount is (a) unit;
70% by weight, (b) unit; 30 to 80% by weight, and (c) unit: 0 to 40% by weight having a radical polymerizable group at one end of a polymer and having a number average molecular weight of 1,000 to 3;
000 macromonomer. 2. The graft copolymer according to claim 1, wherein the proportion of the branch polymer based on the total amount of the backbone polymer and the branch polymer is 0.1 to 0.1.
2. The aqueous coating according to claim 1, wherein at 20% by weight, the proportion of (meth) acrylate monomer units in the backbone polymer is at least 50% by weight based on the total amount of all monomer units forming the backbone polymer. Agent.